Some New Cestodes from New Zealand Marine Fishes
[Received by the Editor February 28, 1958.]
Five new species of cestodes from marine fishes of New Zealand are described: Acanthobothrium wedli from Raja nasuta; Echinobothrium coronatum from Mustelus lenticulatus; Gymnorhynchus (Molicola) thyrsitae from Thyrsites atun; Gymnorhynchus (Gymnorhynchus) isuri from Isurus glaucus; Prochristianella aetobatidis from Aetobates tenuicaudatus.
Relatively few cestodes have been collected from fishes of the southern oceans. In New Zealand up till the present time, cestodes have received scant attention, particularly with regard to the cestodes of marine fishes. In Hutton's “Index Faunae Novae-Zealandiae ” (1904) appears a list of cestodes from New Zealand which includes species recorded from marine fishes.
Leiper and Atkinson (1914) described “a peculiar Tetrarhynchus larva ” from the “barracouta ” Lepidopus caudatus and Perrenoud (1931) described a new species of Acanthobothrium from Trygon pastinaca. Both these host identifications are doubtful.
The five new species of cestodes described were collected during the examination of 206 hosts comprising 46 species of 45 genera of fishes.
No new techniques have been employed for fixing, preserving or staining. Material was fixed in hot 70% alcohol. Histological sections were stained with Ehrlich 's haematoxylin and counter-stained with eosin in 95% alcohol. Type specimens are deposited in the type collection of the Dominion Museum, Wellington, and paratypes in the Department of Zoology, Victoria University College, Wellington.
Family Onchobothriidae Braun, 1900
Acanthobothrium wedli n. sp (Figs. 1–6.)
This species was collected from the spiral valve of Raja nasuta Mueller and Henle. Five adults were collected from a host specimen taken at Petone Beach in November, 1954. Three further specimens were collected from the same host species caught at Portobello, Otago Harbour, in 1952.
The following is an account of the holotype:
The entire worm measures approximately 130.0 mm in length, with a maximum width of 3.0 mm. The rather small scolex 0.47 mm in length is compact with four sessile bothridia. Each bothridium, up to 0.35 mm × 0.23 mm, is divided into three loculi by two muscular septa, the anterior loculus being the largest. The bothridia are muscular with the posterior margins projecting from the surface of the scolex. Anterior to the large loculus, each bothridium bears a pair of bifurcated books 0.097 to 0.105 mm in length. The two prongs of each hook are almost equal in size. There is no accessory sucker anterior to each bothridium Immediately behind the scolex the neck is narrow, but it soon enlarges into a thick tubular region 0.84 mm in diameter which tapers posteriorly. The first proglottids are visible about 7.0 mm posterior to the scolex and are many times broader than long. Near the extreme posterior end of the strobila the acraspedote proglottids become longer than broad. The whole strobila is flat and ribbon-like, with the thread-like everted cirri clearly visible along the lateral margins.
The distinctly two layered cuticle 0.005 mm thick, is usually more conspicuous in cross section near the lateral margins of the proglottis. The musculature consists of a thin layer of extremely fine longitudinal muscle fibres below the cuticle and a well-developed layer of large longitudinal muscle fibres at the junction of the cortex and medulla. The internal fibres are irregularly grouped into fascicles.
In the medulla towards the lateral margins of the proglottis are located the excretory canals. The dorsal canal is the more difficult to identify, but when present is about the same size as the conspicuous ventral canal. Close to each lateral margin of the proglottis is situated a nerve trunk 0.027 mm in diameter.
The testes are arranged in a single, closely packed layer in the medulla, anterior to the ovary. Each irregularly oval testis has a thick muscular wall and measures up to 0.150 mm in width. The testes number 80–100 per proglottis. In the mature region of the strobila, the vas deferens occupies a considerable part of the medulla in the median region of the proglottis. The distal portion of the vas deferens extends laterally, dorsal to the vagina to enter the cirrus pouch. Inside the cirrus pouch, the vas deferens forms a ductus ejaculatorius, which gives rise to the cirrus. When the cirrus is invaginated, the cirrus pouch is distended and rounded, but when evaginated, the pouch is narrow and elongated. The cirrus is a long narrow structure swollen at the base. It has a thick cuticle and is covered by rows of fine hairs.
When the cirrus is invaginated, the enlarged distal portion of the vagina opens into a short genital atrium, situated ventro laterally, near the middle of the margin of the proglottis. However, when the cirrus is evaginated, the distal portion of the vagina is also evaginated, so that it opens anterior to the cirrus on a small papilla. In this way the genital atrium is obliterated and the male and female ducts open to the exterior separately. The vagina passes medially, ventral to the vas deferens, then coils posteriorly to expand into the receptaculum seminis anterior to the ovarian isthmus. The two large, lateral lobes of the ovary are connected medially by the narrow isthmus. The lateral margins of the ovary are distinctly tabulate. From the posterior margin of the isthmus arises the large and extremely muscular oocapt, 0.065 mm in diameter. From the oocapt, the oviduct extends posteriorly to receive the narrow fertilization duct and finally enters the large shell gland. From the shell gland arises the uterine duct which extends anteriorly. The vitelline follicles are arranged in two lateral fields, slightly medial to the nerve trunks. The vitelline ducts and reservoir were not observed.
In the terminal gravid region of the strobila, the uterus distended with eggs, occupies practically the whole of the proglottis. It is not a simple sac-like cavity, but has numerous finger-like extensions which reach the lateral, anterior and posterior margins of the proglottis. In cross-sections of a gravid proglottis, only the cuticle and a thin layer of cortex are present apart from the uterus. The eggs are round, thin-walled, and up to 0.020 mm in diameter.
The following is a description of the two paratypes. The strobila does not appear flat and ribbon-like because of contraction during fixation inside the spiral valve of the host. The scolex is 0.30 mm to 0.36 mm in length and 0.16 mm to 0.23 mm wide at the posterior margin of the bothridia. Except for the strongly projecting posterior margins of the bothridia, the scolex is compact. Each bothridium is divided into three loculi by two transverse muscula septa, towards the posterior margin of the bothridium. Anterior to each bothridium is a pair of stout bifurcated hooks, 0.097 mm to 0.105 mm in length. The hooks are slightly inclined towards each other anteriorly, and consist of a broad base and two almost equal, posteriorly directed prongs. There is an extensive cavity inside the hooks which extends into the prongs. The scolex does not bear any accessory suckers.
Immediately posterior to the scolex, the neck expands into a tubular transversely wrinkled region 7.3 mm to 8.0 mm long and 0.70 mm to 0.94 mm in diameter. In one specimen, the posterior limit of this region is very conspicuous. Throughout the strobila, the size and shape of the proglottids varies considerably due to differences in the degree of contraction. The weakly craspedote nature of the proglottids is much more clearly shown than in the holotype. The total length of the complete worm is 80.0 mm, that of the incomplete specimen approximately 65.0 mm.
The original description of the genus Acanthobothrium by van Beneden (1850), in which he stated the two hooks of each bothridium are united, has been modified by Beauchamp (1905) and Pintner (1928), who agree that although the hooks may be closely approximate, they are not joined. Southwell (1925) and Verma (1928) separate the species of this genus primarily on total hook length. Dollfus (1926), discussing A. crassicolle, considers that hooks of even a single specimen
Text-fig. 1.—Acanthobothrium wedli n. sp. 1, Scolex, lateral view. 2, Mature proglottis. 3, T. S. through cirrus pouch. 4, Gravid proglottis. 5, T. S. posterior to ovarian isthmus. 6, Hooks from anterior margin of bothridium.Echinobothrium coronatum n.sp. 7, Scolex, lateral view. 8, Rostellar hooks. 9, Entire worm. 10, Hooks from Kopfstiel.
are not identical in form and dimensions—a view partially supported by Perrenoud (1931). Also the taxonomic importance of the number and size of the accessory suckers has been questioned by Perrenoud (1931) and others.
Baer (1948), reviewed and revised species of Acanthobothrium and recognises fourteen species with two species inquirendae. Baer considers the total length of the strobila, the number of testes and the ratio of the lengths of the hook handle, internal prong and external prong, to total hook length, as more satisfactory taxonomic characters. Perrenoud (1931) described A. intermedium as a new species from Trygon pastinaca, taken at Tauranga, New Zealand. Baer (1948) lists the host species as Dasyatis pastinaca and regards. A. intermedium Perrenoud, 1931 proper, as identical to A. crassicolle Wedl, 1855.
Acanthobothrium wedli closely resembles.A. microcephalum Alexander, 1953, in the total length of the hooks, the size of the scolex, and the number of testes. In A. wedli, however, accessory suckers are lacking; there is no velum-like fold which attaches the posterior part of each bothridium to the neck; the hook handle is 0.070 mm long, the inner prong 0.027 mm and the outer prong 0.035 mm long, while in A. microcephalum the length of the hook handle is 0.036 mm and the two prongs measure 0.064 mm in length. The strobila of A. wedli is much wider and the testes, up to 0.150 mm in diameter are considerably larger than those of A. microcephalum which are 0.023 mm to 0.038 mm in diameter. Proglottis shape showed so much variation that it is not regarded as significant.
Echinobothrium coronatum n. sp. (Figs. 7–10.)
A single specimen of this species was collected from the spiral valve of Mustelus lenticulatus Phillips from Wellington Harbour in March, 1954. Three detached proglottids were also found in the spiral valve.
The following is an account of the holotype:
The worm is 6.5 mm long and consists of the scolex, a region with longitudinal rows of hooks called the “Kopfstiel” by German writers, and the strobila, which is made up of 21 distinct proglottids.
The two comparatively shallow bothridia 0.380 mm in length, are armed with small spines on their outer surface. Spines do not cover the entire bothridial surfaces, but only occur near the base. Anteriorly, the scolex terminates in a large muscular disc which bears two separate groups of hooks arranged dorsally and ventrally. Some hooks are missing from one of these groups. The central region of the intact group is armed with twenty stout hooks. The largest of these hooks 0.118 mm long are medial, the smallest 0.035 mm long, are lateral. On each side of this central group of stout hooks is a lateral group of 14 fine hooks arranged in two alternate rows and measure up to 0.032 mm in length.
Posterior to the bothridia is a region called the “Kopfstiel”, 1.30 mm in length, which is armed with 8 longitudinal rows of hooks. The largest hooks 0.095 mm in length are situated anteriorly. Each hook consists of a long, straight, tapering shaft and a tri-radiate base which is attached to the surface of the “Kopftsiel”. There are 32 hooks in each row and the size of the hook shaft decreases posteriorly. This region of characteristic hooks is sharply distinguished from the strobila by a constriction.
The strobila is entirely acraspedote and consists of approximately 21 distinct proglottids, and also three detached proglottids. The three detached proglottids are greyish in colour, due to the accumulation of eggs in the uterus In the anterior 0.5 mm of the strobila no proglottids are distinguishable. The first visible proglottids are much broader than long, but soon become square in shape, while the most posterior ones are cylindrical and much longer than broad.
The ovary was clearly visible, situated near the dorsal surface and towards the posterior margin of the proglottis. The genital atrium is on the ventral surface slightly anterior to the ovary. The proximal region of the cirrus pouch is curved anteriorly and contains the cirrus proper, which is covered with bristles. The testes are comparatively large, up to 0.128 mm in diameter, and number 9–11 per proglottis.
Contained in the uterus are the eggs, which are irregular in shape, thin-walled, and up to 0.027 mm in diameter.
This species differs from those previously described in having some more hooks arranged in the two groups at the anterior end of the scolex. There is a total of 42 hooks in the complete group, the largest of which are bigger than any of those previously described. The large size of the hooks on the “Kopfstiel ” and also the large number of hooks making up a longitudinal row, distinguish it from other species. In other species the number of proglottids is smaller.
Family Gymnorhynchidae Dollfus, 1935
Gymnorhynchus (Molicola) thyrsitae n. sp. (Figs. 11–15.)
This larval form was collected from Thyrsites atun (Euphrasen), caught at Cape Campbell, Cook Strait. Twenty-eight host species have been examined, and in all but three this parasite has been found. When present, the number of worms varied between 3 and 286 in different host specimens. The most satisfactory method of counting the larvae was to fillet the fish, and remove the conspicuous opaque blastocysts rather than attempt to remove the parasite in toto. When removed from the flesh of the host and placed in Ringer 's solution, the blastocyst with the invaginated scolex could be seen moving about inside the fibrous outer capsule. Larvae removed from the flesh of the host which had been frozen for 10 days were found to be still alive. In the host specimen with 286 parasites present, only 15 were located in the dorsal muscle mass. Infestation occurred from a level just posterior to the cloaca, to as far forward as the cranium, with a few present also in the throat muscles. This distribution was found to be fairly constant. Although in three host specimens several parasites were found in the caudal region posterior to the cloaca, they were usually found anterior to this region. The region most heavily infested was the muscle near the ventral extremity of the ribs. In all the parasites collected, there were no signs of degeneration of the surrounding muscle, or of the muscle being absorbed by the parasite. From the comparatively few host specimens examined there did not seem to be any particular time of the year when infestation was more marked.
Considerable difficulty was experienced in bringing about the evagination of the proboscides. The most satisfactory method was to leave the larvae in Ringer 's solution for two hours, transfer to water at 65° C. for half a minute, and finally fix in hot 70% alcohol.
The following is an account of the holotype.
When the tough outer capsule was removed, the larva was seen to consist of a globose, densely white blastocyst which contianed the scolex, and a long narrow caudal extension. The extruded scolex is 4.6 mm m length. Anteriorly, the pars bothridialis is the widest region of the scolex, measuring 1.4 mm m width. Each ear-shaped bothridium has an entire margin which is not curled. The bothridia 1.01 mm × 0.63 mm are not inclined towards each other anteriorly and give a distinct “cross ”-shape to the pars bothridialis when viewed from the anterior end. The proboscides arise near the anterior end of the bothridia. The total length of a proboscide (by adding the portion evaginated to the portion invaginated; is 3.20 mm.
When the proboscide is evaginated there is a region at the base, 0.46 mm in length, which is without hooks, but this region was shorter in the remaining proboscides, which were not detached from the scolex. The basal armature is characterised by stout falciform hooks which are arranged around the base except on the middle of the external surface of the proboscide. The largest hooks in this region measure up to 0.135 mm in length, and the smallest hooks, which are the most posterior, measure 0.03 mm. Hooks of intermediate size are situated between them. On the external surface of the proboscide in the basal region are located a large number of hooks with broad bases of implantation, narrow relatively straight shafts and fine tips, which anteriorly merge into the band of fine microhooks.
Anterior to the basal armature, on the internal surface of the proboscide is another characteristic region of hooks arranged in two lateral groups and joined by some reduced hooks. One lateral group consists of obliquely transverse rows of hooks which vary greatly
Text-fig. 2.—Gymnorhynchus (Molicola) thyrsitae n. sp. 11, Entire larva. 12, Scolex and anterior region of blastocyst. 13, Internal surface of distal region of proboscide. 14, External surface of distal region of proboscide. 15, Characteristic armature anterior to the basal region of proboscide.
in shape, as shown in Fig. 8. The hooks of the most anterior rows up to 0.015 mm in length, are stout with a broad base and a low recurved shaft. The most posterior rows consist of hooks up to 0.032 mm in length, with an extremely narrow base, a long narrow shaft and a sharply recurved tip. The group towards the other lateral margin of the internal surface of the proboscide, consists of obliquely transverse rows of hooks which have a constant shape. The broad base of implantation of these hooks is narrow anteriorly and rounded posteriorly, and from the base arises a short, stout shaft.
The hooks of the metabasal region of the proboscide are arranged in obliquely-transverse ascending half turns. Hook 1, 0.050 mm long, is thick and rose-thorn shaped with a strongly-projecting anterior region of the base of implantation. Hooks 1 and 1 ′ are inclined towards each other at the middle of the internal surface of the proboscide. The remaining hooks of the row are falciform and finally decrease in size towards the middle of the external surface. Hooks 2 and 3, 0.067 mm long, have a sharply recurved tip, hooks 4 and 5, 0.075 mm in length, have the tip distinctly flattened, while hooks 6 to 9 show a gradual decrease in length and thickness of the shaft. The middle of the external surface of the proboscide is occupied by a longitudinal band of small hooks, between 0.020 and 0.025 mm long, which have no expanded base of implantation.
Text-fig. 3.—Gymnorhynchus (Gymnorhynchus) isuri n. sp. 16, Scolex, bothridial surface. 17, Scolex, antibothridial surface. 18, T. S. of immature proglottis. 19, Whole mount of immature proglottis. 20, Entire worm. 21, Large hooks on the internal surface of a proboscide. 22, Double chainette on the external surface of a proboscide. 23, Hooks of double chainette. 24, Proximal region of proboscide, external surface. 25, Proximal region of proboscide, internal surface.
The pars vaginalis is not distinguished externally from the pars bulbosa. The pars bulbosa contains the four muscular bulbs, 0.77 mm × 0.26 mm. Internally, the retractor muscle of the proboscide is attached to the posterior wall of the bulb. There is a constriction between the pars bulbosa and pars post bulbosa. The pars post bulbosa is attached to the oval, wrinkled blastocyst which gives rise to a long narrow caudal extension.
Gymnorhynchus (Molicola) thyrsitae n. sp. differs from the other species of this sub-genus—Gymnorhynchus (Molicola) horridus (Goodsir), 1841, in the following characters:
The scolex invaginates in the blastocyst and is not curved around it.
The bothridial margins are not thick and rounded.
The characteristic armature of the internal surface of the proboscide immediately anterior to the basal armature.
The flattened tips of hooks in approximately the middle region of a half-turn of principal hooks.
Gymnorhynchus (Gymnorhynchus) isuri n. sp. (Figs. 16–25.)
A single specimen of this species was collected from the spiral valve of Isurus glaucus (Mueller and Henle) caught at Makara, Cook Strait, in June, 1955.
The bothridia, arranged in pairs on the dorsal and ventral surfaces of the scolex, are muscular and conspicuous. In lateral view the bothridia have strongly projecting, rounded posterior borders. Each bothridium is ear-shaped, measuring 2.66 mm in length and 1.21 mm in width. The bothridial cavities are deep and the bothridial margins are entire and rounded. The pars vaginalis 1.05 mm in length, is followed by the pars bulbosa 3.51 mm in length and slightly swollen in lateral view. The pars post bulbosa is extremely short and its posterior limit is indicated by a slight constriction. The strobila measures 77.0 mm in length and the first visible proglottids appear close to the posterior margin of the pars post bulbosa. Anteriorly the proglottids are much broader than long, but towards the posterior end of the strobila they increase in length until the terminal three proglottids are as long as they are broad.
The proboscides arise from the anterior margins of the bothridia. When the worm was first removed from the spiral valve of the host, the proboscides were invaginated, but when the scolex was placed in warm water they evaginated extremely rapidly.
The length of the proboscides varies between 8.0 mm and 10.2 mm when completely evaginated. When the proboscide is evaginated there is a short region at the base up to 0.6 mm in length which is without hooks. The basal armature consists of a ring of from 13 to 15 hooks of widely varying size. The smallest hooks are situated on the external surface of the proboscide. All the hooks of this region have narrow bases with long, slightly curved shafts and rounded tips. The largest hook in this region measures 0.265 mm. Anterior to the basal armature the hooks are arranged in transversely ascending half turns. The size and shape of the hooks varies at different levels of the proboscide. In the proximal metabasal region up to 2.0 mm in length the hooks have narrow shafts and reduced bases of implantation. In the most distal 1.5 mm of the proboscide the hooks decrease rapidly in size. The following figures apply to hooks between these two regions. There is a narrow region between hooks 1 and 1 ′ (i.e., the middle of the internal surface of the proboscide) which is without hooks. Hook 1 is stout, with a broad base of implantation and thick shaft, measuring up to 0.168 mm in length. Hooks 2 to 6 are finer with a slightly curved shaft and up to 0.140 mm in length.
The remaining hooks in each half-turn become smaller towards the middle of the external surface of the proboscide, with the final hook of the half turn up to 0.085 mm in length. The middle of the external surface possess hooks arranged in a double chainette characteristic of the sub-genus Gymnorhynchus. Each hook consists of a narrow, slightly curved shaft and a base which curves laterally. The convex surface of the hooks of the two rows approach one another. The hooks of the double chainette are up to 0.055 mm in length.
The proboscide sheaths are sinuous but not densely coiled and contain the retractor muscles of the proboscides which are attached to the base of the muscular bulbs.
The internal musculature of the proglottids is well developed. Scattered sub-cuticular muscle fibres are located immediately below the extremely thin cuticle. The deeper musculature consists of a conspicuous layer of longitudinal muscle fibres arranged in fascicles in the cortex. At the junction of the cortex and medulla is a layer of circular muscle fibres. The proglottis musculature is completed by scattered dorso-ventral muscle fibres which extend across the medulla.
The excretory system consists of a pair of longitudinal canals located in the medulla towards the lateral margins of the proglottis. On each side the dorsal canal is much smaller than the ventral canal. Near the posterior margin of the proglottis the large ventral canals
Text-fig. 4. —Prochristianella aetobatidis n. sp. 26, Entire worm. 27, Pars bothridialis and pars vaginalis. 28, Detached muscular bulb. 29, T. S. at level of ovary. 30, T. S. posterior to cirrus pouch. 31, Internal surface of proboscide. 32, External surface near distal extremity of proboscide. 33, Internal surface of basal region. 34, External surface of basal region. Corrigenda: the scales in Figures 29–34 should read 0.1 mm.
are joined by a transverse excretory canal. Lateral to the excretory canals are the longitudinal nerve trunks. Each nerve trunk is a relatively large, fibrous rounded structure, 0.05 mm in diameter.
Some details of the reproductive system are not described as the proglottids had not reached maturity. The testes form a testicular field in the median region of the medulla. From the anterior median region of the proglottis the vas deferens coils laterally and dorsally to enter the cirrus pouch which lacks a muscular wall. The invaginated cirrus was clearly visible but the genital atrium was not seen. Extending ventrally below the cirrus pouch the vagina passes posteriorly to the level of the ovary close to the posterior margin of the proglottis. The incipient uterine pore is located slightly anterior to the proximal margin of the cirrus pouch.
According to Dollfus (1942), a description of an adult belonging to the sub-genus Gymnorhynchus has not been published. Pintner (1929), described a specimen consisting of a scolex and an appendix, but which showed no signs of proglottis formation.
This adult specimen differs from previous descriptions of the larva of Gymnorhynchus (G.) gigas in having the posterior margins of the bothridia of the same face closely approximating. Also, when viewed from above the anterior margin of the scolex, the posterior bothridial margins project strongly. The naked region at the base of the proboscide is much shorter than in G. (G.) gigas. The hooks of the basal armature are fewer in number and clearly differentiated from the metabasal armature. The maximum size of the hooks of the basal armature is larger than that of G. (G.) gigas and although small, hooks are present on the external surface of the proboscide in the basal region. The maximum length of the proboscides is also greater than that of G. (G.) gigas.
Family Eutetrarhynchidae Guiart, 1927, emended Dollfus, 1942
Prochristianella aetobatis n. sp. (Figs. 26–34.)
In March, 1955, a specimen of Aetobatis tenuicaudatus (Hector) was examined. The spiral valve contained a large number of this parasite. When removed from the host and placed in Ringer 's solution, a bright orange-red spot was clearly visible near the posterior region of the pars vaginalis. On preservation the colour rapidly disappeared. The posterior proglottids were often detached from the strobila by agitation of the parasite and many free proglottids were found in the contents of the spiral valve.
The following is a description of the holotype:
The two bothridia are shallow, 0.41 mm in length, with slightly curled margins. In lateral view the two bothridia are inclined towards each other anteriorly. The pars vaginalis 0.784 mm in length is widest immediately behind the bothridia where it measures 0.49 mm. The pars bulbosa is 1.358 mm in length, and is followed by the very short pars post bulbosa. Measurements of the holotype (A) and four paratypes (B-E) are given below:
The formation of proglottids begins almost immediately posterior to the pars post bulbosa. The anterior proglottids are broader than long but posteriorly they increase in length until the most posterior proglottis (i.e., the sixteenth visible proglottis) is 1.15 mm in length and 0.45 mm in width.
The proboscides arise from the anterior margins of the bothridia. The total length of a proboscide is 1.76 mm. In the proximal metabasal region the diameter is 0.07 mm, but decreases to 0.05 mm towards the distal extremity. The basal region of the proboscide is narrow proximally but enlarges distally to a maximum width of 0.085 mm. The basal armature consists of six transversely ascending rows of principal hooks arranged in half turns. These hooks have a broad base, a long narrow shaft and a fine tip. There is a a steady decrease in the size of the hooks from the internal to the external surface of the proboscide. Also on the external surface, at the distal extremity of the basal region are situated three very stout
hooks with an extremely broad base 0.024 mm wide, and a small recurved point. The remainder of the proboscide is armed with obliquely transverse rows of hooks arranged in half-turns, those of one face alternating with those of the other. Each half-turn comprises 12 hooks, the longest of which, 0.036 mm, is near the mid-line of the internal surface, the remaining hooks of the half-turn decreasing regularly towards the external surface of the proboscide. The proboscide sheaths are sinuous without being tightly coiled. When the pro-boscides are invaginated they extend about one-third the distance into the cavity of the muscular bulbs, and are followed by the retractor muscles which are attached to the posterior margin of the bulbar cavity. The muscular bulbs are 1.358 mm in length by 0.15 mm in width.
The proglottis musculature system is poorly developed. Beneath the thin cuticle is a laver of longitudinal subcuticular muscle fibres. Deeper in the cortex are scattered longitudinal and circular muscle fibres.
The excretory system consists of a small dorsal canal and a large ventral canal situated near the lateral margins of the medulla. Lateral to the excretory canals are the longitudinal nerve trunks.
The testes are arranged in two longitudinal rows from the anterior margin of the proglottis to a level just anterior to the ovary. They are relatively large, up to 0.18 mm deep, with a thick muscular wall. The vas deferens is a tightly coiled duct which arises at the level of the ovary and extends anteriorly then laterally to expand into an external seminal vesicle, before entering the cirrus pouch. The large ductus ejaculatorius contains the invaginated cirrus.
The genital atrium opens at the lateral margin at about the beginning of the posterior third of the proglottis. The distal extremity of the vagina has a thick muscular wall and opens into the genital atrium ventral to the cirrus pouch. The vagina extends posteriorly in the ventral region of the medulla to a level slightly anterior to the ovarian isthmus, where it expands into the receptaculum seminis. The ovary, which occupies most of the medulla consists of four large lobes joined by the ovarian isthmus. From the receptaculum seminis the fertilization duct passes dorsally over the ovarian isthmus and then ventrally to join the oviduct. The oviduct arises on the ventral surface of the ovarian isthmus at the muscular oocapt It then extends posteriorly and receives firstly the fertilization duct and then the vitelline reservoir before entering the shell gland. From the shell-gland, the uterine duct extends anteriorly and gives rise to the uterus. Even in the most posterior proglottis the uterus did not contain any eggs. The vitellaria occupy most of the cortex anterior to the ovary.
Dollfus (1957) notes that the name of the type species of the genus Prochristianella is P. papillifer (Poyarkoff, 1909). P. aetobatidis differs from P. papillifer in the following respects: (1) the proboscides are approximately only half the length, (2) the basal armature consists of six rows of hooks arranged in half-turns, (3) three characteristic hooks are present at the junction of the basal and metabasal regions, (4) the metabasal armature does not show the increase and subsequent decrease in the size of the hooks.
From the short description of Linton (1890) and that of Dollfus (1946), ? Prochristianella tenuispinis (Linton, 1890) differs from P. aetobatidis particularly in hook size and arrangement.
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E. S. Robinson,
The University of Nebraska, Department of Zoology, Lincoln 8, Nebraska, U.S.A
Explanation of Text-Figs.
The following abbreviations are used in Text-fig. 1–4: —
BA, basal armature
CE, caudal extension of blastocyst
CP, cirrus pouch
DC, double chainette
DEX, dorsal excretory canal
DE, ductus ejaculatorius
EXC, excretory canal
FD, fertilization duct
LM, longitudinal muscle
MB, muscular bulb
NT, nerve trunk
PBL, pars bulbosa
PS, proboscide sheath
PV, pars vaginalis
RM, retractor muscle
SH, shell gland
TEX, transverse excretory canal
UP, uterine pore
UTD, uterine duct
VD, vas deferens
VEX, ventral excretory canal
VR, vitelline reservoir.